Trill is a world best known for its "joined"
inhabitants, the beneficiaries of an intimate symbiotic union between the
planet's two sentient life-forms, the humanoid Trill
and
a species of small vermiform symbionts. Most of the personality traits
and memories of the combined life-form are contributed by the symbionts,
who are extremely long lived.

So while a visitor to Trill might think
he is speaking with a young man, he may actually be conversing with an
accumulation of personalities- only some of which may be male and almost
none of which are young. In effect, the symbionts are living time capsules,
preserving the calues and customs of Trill
antiquity.